Percutaneous transluminal coronary angioplasty (PTCA) can cause the denervation of epithelium and the injury to medial vascular smooth muscle cells (VSMCs). In response to the imposed injury, VSMCs migrate from the media to the intima, which is an important pathogenic event of restenosis. Preliminary studies with use of flow channel show that the Cbl, which is a proto-oncogene product (Sasitas B-lineage lymphoma), and is the cellular homology of the alcoprotein b-Cbl, scaffolding molecule and Rho and Rac GTPases play clinical roles in enhancing VSMC migration in response to shear stress. Thus, we hypothesize that integrins in VSMCs serve as mechanotransducers by dynamically interacting with specific extracellular matrices (ECMs). As a result, Cbl is tyrosine-phosphorylated to form a complex with PI3K and Vav2, which, in turn, activates the Rho-ROCK and Rac-gelsolin pathways. The coordination of these two pathways enhances the migration of VSMCs. Four Specific Aims are proposed to test our hypotheses. Specific Aim 1 is to elucidate the roles of integrin in shear stress enhancement of VSMC migration. Specifically, we will study the mechanically sensitive integrins and VSMCs, and the test the hypothesis that a specific and dynamic interaction between these integrins and their cognate ECMs is important in augmenting VSMC migration. Specific Aim 2 is to delineate the molecular mechanisms by which Cbl activates Rho and Rac to enhance VSMC migration. Specifically, we will examine whether the Cbl functions as a scaffolding molecule to dock PI3K and Vav2 in activating Rho and Rac, and investigate whether shear stress activation of Cbl-PI3K-Vav2 depends on integrin and ECM interaction. Specific Aim 3 is to determine the roles of the Rho-ROCK and Rac-gelsolin signaling pathways in shear stress enhancement of VSMC migration. Specifically, we will explore the role of Rho in activating ROCK, and the role of Rac in activating gelsolin to enhance VSMC migration. Specific Aim 4 is to investigate the roles of Cbl, Rho, and Rac in VSMC migration in rat carotid arteries after balloon angioplasty. Specifically, we will examine the activation of Cbl, Rho and Rac in injured vessels and test the efficacy of using negative and active mutants of these molecules to inhibit or enhance VSMC migration in vivo. With strong interaction between Bioengineering, Surgery and Biomedical Sciences, as well as in vitro and in vivo approaches this proposal will generate new information relevant to mechanotransduction in VSMCs and pathophysiology of restenosis.